Hypophosphataemia after intravenous iron therapy with ferric carboxymaltose—Real world experience from a tertiary centre in the UK

Background Iron deficiency is the most common global cause of anaemia. Intravenous (IV) iron is used to correct iron deficiency anaemia (IDA) where oral iron cannot be used. Despite being effective, certain IV iron formulations cause significant hypophosphataemia. However, current knowledge on the clinical consequences of IV iron-induced hypophosphataemia is broadly anecdotal or limited to isolated case reports. Aims To retrospectively examine the incidence and potential clinical consequences of hypophosphataemia post-IV ferric carboxymaltose (FCM) in hospitalised patients with IDA (mixed aetiology). Methods Data were collected for 162 patients, who received a total of 169 FCM courses during a 2-year audit period. Outcomes included incidence of moderate/severe hypophosphataemia (serum phosphate <0.65 mmol/L) ≤90 days post-FCM, changes in alkaline phosphatase, need for phosphate replacement, and length of hospital stay. Results The incidence of moderate/severe hypophosphataemia post-FCM was 33.7%; within this group the rate of severe hypophosphataemia (serum phosphate ≤0.32 mmol/L) was 8.8%. Moderate/severe hypophosphataemia persisted, with 35% of patients having a serum phosphate of <0.65 mmol/L for ≤90 days at the last measurement after IV FCM. Intervention with IV phosphate—an average of 4.4 infusions per person—was required in 29.8% of cases with moderate/severe hypophosphataemia. FCM-induced moderate/severe hypophosphataemia was associated with a significantly longer hospital stay (P < 0.0035). Conclusions Moderate/severe hypophosphataemia is a frequent adverse drug reaction with FCM. In our study, FCM-induced moderate/severe hypophosphataemia was also persistent, often required treatment, and was associated with longer hospital stay.